Conventional laser-arc welding devices operate by projecting a laser beam from a laser source onto a worksite of a workpiece and striking an arc between an electrode of the arc welder and the worksite.
This is shown for example in FIG. 1A, wherein reference numeral 1 refers to a laser head including a support structure 2 and a focusing lens 3 for focusing a laser beam 4 onto a worksite 5 of a workpiece 6. The incident laser beam 4 heats the worksite 5 and an arc welding torch 7 arcs current from an electrode 8 to the worksite 5 to provide the welding or cutting operation.
As shown in FIG. 1A, the arc welding torch 7 can be provided on the same side of the workpiece 6 as is the laser head 1. However, as shown in FIG. 1B, if the workpiece 6 is sufficiently thin to allow proper heating of the worksite 5 the arc welding torch 7 may be provided on the opposite side of the workpiece 6 from the laser head 1 so as to make the system more flexible. Further, in these conventional devices some type of electro-mechanical control (not shown) is provided in order to move the workpiece 6 with respect to the stationary laser head 1 and arc welding torch 7 or to move the laser head 1 and arc welding torch 7 with respect to the stationary workpiece 6.
In operation, the incident laser beam 4 of a conventional laser-arc welding device causes the worksite 5 to melt and vaporize which in turn causes a molten material and a plasma cloud to exist at the worksite 5. Additional energy is provided to the worksite 5 by the arc current from the electrode 8 which tends to root along the plasma cloud to the worksite 5. In other words, the plasma cloud caused by the heated worksite 5 provides a low resistance, conductive path for the arc current from the electrode 8 of the arc welding torch 7 to the worksite 5.
In these conventional devices, the laser beam and the arc current from the arc welder are operated continuously to allow both sources of energy to perform the welding or cutting operation at the same time. However, this continuous operation creates a significant problem in that while the plasma cloud initially provides a low resistance, conductive path to couple the arc energy to the worksite, it has been found that this initial efficient coupling is quickly dissipated as the welding operation continues. In particular, as the laser beam or arc remains on, the plasma cloud becomes more highly ionized and introduces a great deal of attenuation into the incident laser beam path. This in turn prevents the laser beam from efficiently heating the worksite 5 by reducing the strength of the laser beam.
This problem is significantly magnified when using highly reflective metals such as aluminum and copper which are most commonly used today as workpiece metals. These highly reflective metals produce a near 180.degree. phase shift in the incident wave, significantly reducing the field strength of the light beam at the work surface. An example of this application might be the welding of a flexible printed circuit-ribbon conductor to a linear multi-pin connector. If copper or aluminum are used as the conductors, it becomes very difficult to couple the optical energy from the laser beam to the weldsite between the conductors and connectors. Further, in welding these very small weldsites, it is important to control both the timing and location in applying the optical and electrical energy because these small weldsites can be completely melted if excessive energy is applied.
Thus, conventional laser-arc welding devices suffer from the disadvantage of being extremely costly because the continuous laser energy applied to the worksite is very expensive. Further, due to the reflectivity of the workpiece, it may be necessary for the laser beam to be operated at close to maximum output in order to couple enough energy into the workpiece. This, of course, reduces the life expectancy of the laser source.
Some conventional laser-arc welding devices attempt to overcome the foregoing plasma interference problems by utilizing an inert gas directed at the worksite to blow away the plasma cloud so as to limit the interference with the incident laser beam. However, as indicated above, this plasma cloud has significant advantages in conducting and rooting the arc current from the arc welding torch to the worksite. Therefore, dissipating the plasma cloud also eliminates the advantages that accompany it.